In integrated circuit manufacturing, a conductive material, such as copper, is often deposited by electroplating onto a seed layer of metal to fill one or more recessed features on the semiconductor wafer substrate. Electroplating is a method of choice for depositing metal into the vias and trenches of the wafer during damascene processing, and is also used to fill Through-Silicon Vias (TSVs), which are relatively large vertical electrical connections used in 3D integrated circuits and 3D packages.
During electroplating, electrical contacts are made to the seed layer (e.g., a conformally deposited copper layer) at the periphery of the wafer, and the wafer is electrically biased to serve as a cathode. The wafer is brought into contact with an electroplating solution, which contains ions of metal to be plated and an acid that provides sufficient conductivity to the electroplating solution. The plating solutions may also contain additives, known as accelerators, suppressors, and levelers that modulate electrodeposition rates on different surfaces of the substrate. Electroplating is typically conducted for an amount of time that is sufficient to fill the recessed features with metal. Then, the unwanted metal deposited on the field regions of the wafer is removed in a planarization operation, such as by a chemical mechanical polishing (CMP).
One of the problems encountered during electroplating is non-uniform distribution of thickness of electrodeposited metal along the radius of the circular semiconductor wafer. This type of non-uniformity is known as radial non-uniformity. Radial non-uniformity may occur due to a variety of factors, such as due to a terminal effect, and due to variations in electrolyte flow at the surface of the substrate. Terminal effect manifests itself in edge-thick electroplating, because the potential in the vicinity of the electrical contacts at the edge of the wafer can be significantly higher than at the center of the wafer, particularly if a thin resistive seed layer is used. An ionically resistive ionically permeable plate positioned in the proximity of the wafer substrate can mitigate the terminal effect. The plate is typically made of a resistive material and includes a plurality of channels through which the electrolyte is transported towards the wafer substrate. The plate introduces an additional resistance into the plating cell which leads to reduction of terminal effect. This plate can also serve as a flow-shaping element for distributing the flow of electrolyte. In a conventional system the flow-shaping element includes a large number of uniformly distributed isolated channels of the same size. The channels are perpendicular to the plating face of the wafer substrate and provide an impinging flow of electrolyte to the substrate.